Changing field::field_name and Item::name to LEX_CSTRING

Benefits of this patch:
- Removed a lot of calls to strlen(), especially for field_string
- Strings generated by parser are now const strings, less chance of
  accidently changing a string
- Removed a lot of calls with LEX_STRING as parameter (changed to pointer)
- More uniform code
- Item::name_length was not kept up to date. Now fixed
- Several bugs found and fixed (Access to null pointers,
  access of freed memory, wrong arguments to printf like functions)
- Removed a lot of casts from (const char*) to (char*)

Changes:
- This caused some ABI changes
  - lex_string_set now uses LEX_CSTRING
  - Some fucntions are now taking const char* instead of char*
- Create_field::change and after changed to LEX_CSTRING
- handler::connect_string, comment and engine_name() changed to LEX_CSTRING
- Checked printf() related calls to find bugs. Found and fixed several
  errors in old code.
- A lot of changes from LEX_STRING to LEX_CSTRING, especially related to
  parsing and events.
- Some changes from LEX_STRING and LEX_STRING & to LEX_CSTRING*
- Some changes for char* to const char*
- Added printf argument checking for my_snprintf()
- Introduced null_clex_str, star_clex_string, temp_lex_str to simplify
  code
- Added item_empty_name and item_used_name to be able to distingush between
  items that was given an empty name and items that was not given a name
  This is used in sql_yacc.yy to know when to give an item a name.
- select table_name."*' is not anymore same as table_name.*
- removed not used function Item::rename()
- Added comparision of item->name_length before some calls to
  my_strcasecmp() to speed up comparison
- Moved Item_sp_variable::make_field() from item.h to item.cc
- Some minimal code changes to avoid copying to const char *
- Fixed wrong error message in wsrep_mysql_parse()
- Fixed wrong code in find_field_in_natural_join() where real_item() was
  set when it shouldn't
- ER_ERROR_ON_RENAME was used with extra arguments.
- Removed some (wrong) ER_OUTOFMEMORY, as alloc_root will already
  give the error.

TODO:
- Check possible unsafe casts in plugin/auth_examples/qa_auth_interface.c
- Change code to not modify LEX_CSTRING for database name
  (as part of lower_case_table_names)

sql/sql_udf.cc

@@ -54,12 +54,12 @@ static HASH udf_hash;
 static mysql_rwlock_t THR_LOCK_udf;
 
 
-static udf_func *add_udf(LEX_STRING *name, Item_result ret,
-                         char *dl, Item_udftype typ);
+static udf_func *add_udf(LEX_CSTRING *name, Item_result ret,
+                         const char *dl, Item_udftype typ);
 static void del_udf(udf_func *udf);
 static void *find_udf_dl(const char *dl);
 
-static char *init_syms(udf_func *tmp, char *nm)
+static const char *init_syms(udf_func *tmp, char *nm)
 {
   char *end;
 
@@ -192,7 +192,7 @@ void udf_init()
   while (!(error= read_record_info.read_record(&read_record_info)))
   {
     DBUG_PRINT("info",("init udf record"));
-    LEX_STRING name;
+    LEX_CSTRING name;
     name.str=get_field(&mem, table->field[0]);
     name.length = (uint) strlen(name.str);
     char *dl_name= get_field(&mem, table->field[2]);
@@ -242,7 +242,8 @@ void udf_init()
     }
     tmp->dlhandle = dl;
     {
-      char buf[SAFE_NAME_LEN+16], *missing;
+      char buf[SAFE_NAME_LEN+16];
+      const char *missing;
       if ((missing= init_syms(tmp, buf)))
       {
         sql_print_error(ER_THD(new_thd, ER_CANT_FIND_DL_ENTRY), missing);
@@ -311,9 +312,9 @@ static void del_udf(udf_func *udf)
       The functions will be automaticly removed when the least threads
       doesn't use it anymore
     */
-    char *name= udf->name.str;
+    const char *name= udf->name.str;
     uint name_length=udf->name.length;
-    udf->name.str=(char*) "*";
+    udf->name.str= "*";
     udf->name.length=1;
     my_hash_update(&udf_hash,(uchar*) udf,(uchar*) name,name_length);
   }
@@ -351,6 +352,7 @@ udf_func *find_udf(const char *name,uint length,bool mark_used)
 {
   udf_func *udf=0;
   DBUG_ENTER("find_udf");
+  DBUG_ASSERT(strlen(name) == length);
 
   if (!initialized)
     DBUG_RETURN(NULL);
@@ -362,8 +364,7 @@ udf_func *find_udf(const char *name,uint length,bool mark_used)
   else
     mysql_rwlock_rdlock(&THR_LOCK_udf);  /* Called during parsing */
 
-  if ((udf=(udf_func*) my_hash_search(&udf_hash,(uchar*) name,
-                                      length ? length : (uint) strlen(name))))
+  if ((udf=(udf_func*) my_hash_search(&udf_hash,(uchar*) name, length)))
   {
     if (!udf->dlhandle)
       udf=0;					// Could not be opened
@@ -395,7 +396,7 @@ static void *find_udf_dl(const char *dl)
 
 /* Assume that name && dl is already allocated */
 
-static udf_func *add_udf(LEX_STRING *name, Item_result ret, char *dl,
+static udf_func *add_udf(LEX_CSTRING *name, Item_result ret, const char *dl,
 			 Item_udftype type)
 {
   if (!name || !dl || !(uint) type || (uint) type > (uint) UDFTYPE_AGGREGATE)
@@ -431,7 +432,7 @@ static int mysql_drop_function_internal(THD *thd, udf_func *udf, TABLE *table)
 {
   DBUG_ENTER("mysql_drop_function_internal");
 
-  char *exact_name_str= udf->name.str;
+  const char *exact_name_str= udf->name.str;
   uint exact_name_len= udf->name.length;
 
   del_udf(udf);
@@ -548,7 +549,8 @@ int mysql_create_function(THD *thd,udf_func *udf)
   }
   udf->dlhandle=dl;
   {
-    char buf[SAFE_NAME_LEN+16], *missing;
+    char buf[SAFE_NAME_LEN+16];
+    const char *missing;
     if ((missing= init_syms(udf, buf)))
     {
       my_error(ER_CANT_FIND_DL_ENTRY, MYF(0), missing);
@@ -604,7 +606,7 @@ err:
 }
 
 
-int mysql_drop_function(THD *thd,const LEX_STRING *udf_name)
+int mysql_drop_function(THD *thd, const LEX_CSTRING *udf_name)
 {
   TABLE *table;
   TABLE_LIST tables;